It is known to use water as a mechanical blowing agent in the extrusion of thermoplastic elastomer foam, and particularly the extrusion of such structures. Water is a desirable blowing agent, at least in part because it is non-toxic. Known methods of water blowing thermoplastic elastomers typically introduce the water to the thermoplastic elastomer after the thermoplastic elastomer has melted. Experience with extruding thermoplastic elastomer foam using water as a blowing agent has shown that certain extrusion profiles can be extruded at a rate of 40 to 80 feet per minute.
It is known how to produce low density foams from thermoplastic elastomers using water as a blowing agent which have certain compression or deflection rates, and compression set values, and low water absorption characteristics. However, simpler methods, not requiring the post-melt introduction of water, are sought.
It is desired to have a process for forming thermoplastic elastomer foam with water as a blowing agent suitable for use at increased extrusion speeds.
It is also desired to have a process for foaming thermoplastic elastomer foam which provides better control of the cell structure and the skin characteristics.
It is also desired to have a process for forming thermoplastic elastomer foam in which the water is introduced to the extruder simultaneous with the thermoplastic elastomer.